basic ideas about atoms

• What are the main components of an atom?

  An atom consists of a nucleus made up of protons and neutrons, surrounded by electrons.
• Where is most of an atom's mass located?

  Almost all of the atom's mass is in the nucleus.
• How many protons and electrons does an atom have?

  An atom has the same number of protons and electrons.
• What is the atomic number of an element?

  The atomic number is the number of protons in the nucleus of an atom.
• What does the symbol ¹⁹₉F represent?

  It represents fluorine, where 9 is the atomic number and 19 is the mass number.
• What are isotopes?

  Isotopes are atoms having the same number of protons but different numbers of neutrons.
• Give an example of isotopes of chlorine.

  Naturally occurring chlorine consists of two isotopes: ³⁵Cl and ³⁷Cl.
• How do positive ions (cations) form?


  Positive ions form when an atom loses one or more electrons.
• How do negative ions (anions) form?

  Negative ions form when an atom gains one or more electrons.
• What does the atomic number equal in an atom?

  The atomic number equals the number of protons in an atom.
• What is the mass number of an atom?

  The mass number is the number of protons plus the number of neutrons in the nucleus of an atom.
• What happens to the mass number and atomic number when an α particle is emitted?

  The mass number decreases by 4 and the atomic number decreases by 2.
• What is the effect of β particle emission on mass number and atomic number?


  The mass number remains unchanged and the atomic number increases by 1.
• What occurs during electron capture?

  The mass number remains unchanged and the atomic number decreases by 1.
• What is the definition of half-life?

  Half-life is the time taken for half the initial quantity of a radioactive substance to decay.
• Why are radioactive emissions potentially harmful?

  They can break chemical bonds in cell molecules, leading to DNA changes, mutations, and cancer.
• How does the danger of α-emitting isotopes compare to β-emitting or γ-emitting isotopes when ingested?

  α-emitting isotopes are far more dangerous when ingested than β-emitting or γ-emitting isotopes.
• What is the definition of an atomic orbital?

  An atomic orbital is a region in an atom that can hold up to two electrons with opposite spins.
• What is the maximum number of electrons that can occupy an s subshell?

  The maximum number of electrons in an s subshell is 2.
• How many electrons can a p subshell hold?

  A p subshell can hold a maximum of 6 electrons.
• How many electrons can a d subshell hold?

  A d subshell can hold a maximum of 10 electrons.
• What are the types of radioactive emissions and their characteristics?

  • **α particles**: Clusters of 2 protons + 2 neutrons; positively charged; least penetrating; stopped by paper.
  • **β particles**: Fast-moving electrons; negatively charged; attracted to positive plate; stopped by thin metal.
  • **γ rays**: High-energy electromagnetic radiation; no charge; most penetrating; requires lead to stop.
• What are the effects of α and β emissions on atomic and mass numbers?

  • **α emission**: Mass number decreases by 4, atomic number decreases by 2.
  • **β emission**: Mass number unchanged, atomic number increases by 1.
• What are the beneficial uses of radioactivity?

  • Medicine: Cobalt-60 for cancer treatment, Iodine-131 for thyroid studies, Technetium-99m as a tracer.
  • Radio-dating: Carbon-14 for dating remains, Potassium-40 for geological age estimation.
  • Analysis: Dilution analysis and monitoring thickness of materials.
• What is the structure of electron shells and subshells?

  • Electrons occupy fixed energy levels or shells (1, 2, 3...).
  • Each shell contains atomic orbitals grouped in subshells (s, p, d, f).
  • Maximum electrons: s = 2, p = 6, d = 10.
• What is the significance of the Pauli exclusion principle in electron configuration?

  • Two electrons in the same orbital must have opposite spins.
  • This principle helps reduce repulsion between electrons.
• How does the arrangement of electrons in the periodic table relate to their subshells?

  • Elements are classified based on their outer electron configuration.
  • s -block: Outer electron in s orbital.
  • p -block: Outer electron in p orbital.
• How many electrons can the *s* subshell hold?

  2 electrons
• How many electrons can the *p* subshell hold?

  6 electrons
• How many electrons can the *d* subshell hold?


  10 electrons
• What is the classification of sodium and chlorine based on their outer electrons?

  • Sodium is an *s*-block element (outer electron in *s* orbital).
  • Chlorine is a *p*-block element (outer electron in *p* orbital).
• What is the definition of electronic configuration?

  It is the arrangement of electrons in an atom.
• Which orbitals are filled before the 3d orbitals?

  The 4s orbitals are filled before the 3d orbitals.
• What is the electronic configuration of calcium with 20 electrons?

  1s²2s²2p⁶3s²3p⁶4s²
• How is the electron configuration represented using 'electrons in boxes'?

  Each orbital is represented as a box and the electrons as arrows in the boxes.
• How do positive ions form in terms of electron configuration?

  Positive ions form by the loss of electrons from the highest energy orbitals.
• How do negative ions form in terms of electron configuration?

  Negative ions form by adding electrons to the highest energy orbitals.
• What is the equation for the first ionisation energy (IE) of an element?

  X(g) → X⁺(g) + e⁻
• What factors affect ionisation energy?

  Nuclear charge, electron shielding, and distance of outer electron from nucleus.
• What is electron shielding?

  It is the repulsion between electrons in different shells.